This invention relates to the production of new bacterial strains of butanol and acetone-producing bacteria with improved growth characteristics.
At the present time, butanol and acetone can be produced by biological processes by incubating feedstock material, including molasses, corn steep liquor or other carbohydrates, with a variety of strains of Clostridium acetobutylicum and related saccharolytic clostridia. However, the wild type strains of C. acetobutylicum characteristically degenerate, that is, lose the capacity to produce solvents and to sporulate. This phenomenon occurs upon repeated subculture of growing clostridial cells. Degenerate cells cannot switch from producing acids to producing solvents and spores, and therefore, die. Degeneration thus limits the length of time one can use the cells without restarting the cultures by germinating spores. Different wild type strains of C. acetobutylicum degenerate at different rates.
Accordingly, it would be desirable to obtain degneration-resistant mutants capable of producing butanol and acetone from commonly available feedstocks. Such microorganisms would be capable of producing these desired chemicals over extended time periods while reducing the frequency of restarting the culture. Such strains also are useful for development of fermentation by continuous cultures or immobilized solventogenic clostridia. Furthermore, it would be desirable to have a means for producing these mutant microorganisms, employing procedures for identifying and selecting microorganisms with the desired longevity characteristics.